1. Field of the Invention
The present invention relates to a plasma processing method and a computer storage medium.
2. Description of the Related Art
In a recent semiconductor device, a thickness reduction of a gate insulation film is required to improve an operating speed. However, for example, a conventional silicon oxide film has a problem that a thickness reduction results in an increased leakage current and boron contained in an electrode material penetrates the insulation film, which is not desirable. Therefore, adopting an oxynitride film that is thin yet has a prescribed insulative property and can reduce the diffusion of boron has been considered.
For forming an oxynitride film, there has been proposed a method in which an oxide film, after being formed, is plasma-nitrided by a plasma processing apparatus utilizing a microwave, thereby forming the oxynitride film (Japanese Patent Application Laid-open No. 2002-208593). In such a case, the microwave is continuously supplied to generate plasma.
Such a method of forming the oxynitride film by the plasma nitridation process can achieve the same level of a flat band voltage as that of a thermal oxide film since nitrogen distribution can be made higher on an electrode (surface) side, and because of the above reason, can utilize an advantage of plasma that, for example, the diffusion of impurities is easily stopped on the surface side.
Since a plasma nitridation process causes damage due to plasma used therein, an annealing process is performed thereafter. A conventionally adopted annealing process of this type is a so-called “strong annealing process” in which a substrate is heated at about 1100° C. to 1200° for 31 seconds to 60 seconds in a substantially atmospheric-pressure atmosphere. However, during such a strong annealing process, oxygen diffuses due to the annealing process to increase film thickness and thus a dielectric constant lowers, which may possibly result in a lower operating speed and may possibly deteriorate a characteristic against NBTI (Negative Bias Temperature Instability: a phenomenon that deterioration in a source-drain ON current or shifting of a threshold value in a negative direction occurs with time when a negative voltage and continuous temperature stress of about 100° C. are given to a gate of a PMOSFET (instability under negative voltage/high-temperature stress)) which is distinguished especially in a PMOSFET. Therefore, there is a demand for an art utilizing an advantage of microwave plasma with low electron temperature and eliminating a need for a strong annealing process after such a plasma nitridation process.
Further, it has been conventionally difficult to improve both a static characteristic (gate leakage current, source-drain ON current) and NBTI resistance of a transistor in which nitrogen is introduced in a gate oxide film.